Braun tube



April 13, 1937. K; scHLEslNGER" BRAN TUBE Filed July 15, 1933 /n ver? form' Patented Apr. 13, 1937 UNITED sTATEs PATENT OFFICE Application July 15, 1933, Serial No. 680,584 In Germany July 19, 1932 3 Claims.

In the case of Braun tubes for oscillographic and television purposes with electrostatic deflection of .the ray it is well known that if the same are not mirrored on the inside, or furnished with conductance towards the outside at the screen, the electrons, after meeting against the luminous screemcommence to return to the anode in the form of a diffuse return current. It is known that the same, when traversing the space between the deflectng plates, may under certain circumstances cause disturbances in the 'deflectiom and it is also possible, by means of special screening electrodes, which are intended to withhold the return-'flow electrons from the plate space, to overcome these disturbances.

It is more simple to metallize the screen of the cathode ray tube, and to link up the same with the maximum positive potential occurring. It .is also of advantage to mirror not only the screen, but also the entire bulb ofthe tube on the inside down to the neckportion, and to raise this entire coating to the anode potential.

It has been found, however, that by making the bulb reflectory 'in this fashion the sharpness of the image point is liable to sufier.

The present invention overcomes this drawback. The bulb of the tube, as shown in 'the figure, is furnished from the screen I to the neck portion 2 with an inner metallic conductive coating, which is indicated in the drawing by the shaded portion 3 and 4. This coating consists of two parts which are separated from each other by a non-conductive strip 6.

'The coating, for example, may be produced ess, but naturally also in other ways, for example by coating the strip with parafiine, which is later distilled away, prior to the metallizing process, or by preventing the rstrip in any other desired fashion from entering into 'contact at all 'with the coating (mirror'ing) material. The two portions of the coatingy 3 and 4 are linked up with the terminals- 'l and 8. There is then applied to the terminals 1 the highest positive potential occurrlng. This is the potential of the final tube anode 9, which is usually passed to the coating 3 a still higher (more positive) constant potential. To the neck coating 4, however, there will be applied, in accordance with the'invention, a considerably lower potential, for example the potential of the preliminary anode of the tube, which accordingly possesses a strong negative bias in relation to the ray. By exact adjustment of .this bias of the wall coating (for example, with the assistance of a potentiometer) it is possible to obtain an excellent concentration of the ray, as the funnel-shaped electrostatic field resulting within the bulb between 4 and 3 cxerts an exceedingly powerful concentrating effeet. At the same time a return fiow within the tube is prevented by the leakage conductance of the screen, and together therewith there also disappear the known disturbing errors in deflection. Finally, it is also accomplished by reason of the invention that the halo always surrounding the image point is greatly reduced, as a result of which an appreciable advantage is obtained in connection with television tubes.

When employing the arrangement acording to the invention it is possible, particularly when employing two or more Wehnelt cylinder anode systems (indicated in the drawing in dotted lines) or other suitable concentrating means, to produce cathode ray tubes, which also operate well, i. e., with an excellent sharpness of the image pointyeven in the case of high vacuum i. e., gas pressures of the order of -5-10-6 mm. Hg, and normal low anode potentials.

The Optimum potentials of the luminous screen and the intermediate electrode vary in each particular case dependent on the form of the tube, etc., but may be readily determined by way of experiment. In a tube, the diameter of the image screen of which amounted to 125 mm.,`and the length of which amounted to 480 mm., completely sharp image points resulted for example with an 'image screen potential of 3,000 volts if the intermediate electrode had` a potential of approximately 1,000 volts.

The effect according to the invention may naturally be still further increased by particularly favourable form of the intermediate electrode (i. e., if, therefore, there is employed as intermediate electrode a metallic coating on the wall of the tube itself), for example by the use of correspondingly bulging tubes or the like.

By reason of the arrangement according to the invention it is possible for the first time to employ for television purposes and the like high vacuum tubes Operating with low potentials.

I claim:

1. In combination a Braun tube comprising an evacuated envelope, a cathode and an anode arranged in operative relationship thereto for producing a cathode ray, means to control the intensity of the cathode ray, a fiuorescent screen, mean for defiecting the cathode ray in two directions at right angles to each other for scanning the fiuorescent screen, means for concentrating the cathode ray, said concentrating means being arranged between said cathode and said defiecting means, further concentrating means comprising an electrode located inside said Braun tube at a smaller distance from said fiuorescent screen than said defiecting means and said anode, and a further electrode insulated from the first said one r and arranged between the first said electrode and the fiuorescent screen; means to supply the anode with a high positive potential; means to supply the first said electrode with a potential which is negative in comparison to said anode potential; and means to supply the further said electrode with a potential which is positive in comparison to the potential which the first said electrode is to be supplied with.

2. In combination a Braun tube comprising an .v evacuated envelope, a cathode, a Wehnelt-cylinder surrounding said cathode, a first anode arranged in operative relationship to said cathode for producing a cathode ray, a fiuorescent' screen, a second anode arranged between said first anode and said fiuorescent screen, two pairs of deflecting plates arranged between said second anode and said fiuorescent screen, concentrating means comprising a metallic coating arranged on the wall of said envelope between said deflecting plates and said fiuorescent screen, and a second w metallic coating insulated from the first said one and arranged on the wall of said envelope between said first coating and said fiuorescent screen; means to connect said first wall coating with said first anode; means to connect said second wall coating with said second anode; means to supply said Wehnelt-cylinder with a control voltage; means to supply said first anode with a positive potential in relation to said cathode; and means to supply said second anode with a potential which is more positive than the potential said first anode is to be supplied with.

3. In combination a Braun tube comprising an evacuated envelope, a cathode, a fiuorescent screen, three anodes arranged between said cathode and said fiuorescent screen, and two concentrating electrodes, each of said concentrating electrodes being arranged between two of said anodes; means to supply each of said anodes with a positive potential in relation to said cathode, and means to supply each of said concentrating electrodes with a potential which is more negative than the potential which therespective adjacent anode located on the cathode side of said last mentioned concentration electrode is to be supplied with.

KURT SCHLESINGER. 

